The operational requirements of combustion engines are becoming more and more demanding and this the accuracy and reliability of control systems is ever more important. An extremely important fluid flow system in connection with an internal combustion piston engine is the charge air—exhaust gas flow system i.e. the engine gas exchange system. In the efficiently operating internal combustion piston engines, it is almost a rule to use charge air compressors, typically turbochargers, in connection with the engines. In order to operate the engine properly and efficiently over a wide load range means that control of the gas flow is needed at least to some extent. Therefore the turbo charger is often provided with a so called waste gate. The waste gate is a bypass channel over the turbine part of the turbocharger through which a controllable amount of exhaust as may be led without performing work in the turbine part of the turbo charger. The waste gate is typically provided with a mechanical valve, the opening or closure state of which is depending e.g. on the charge air pressure or the engine load. The valve is operating in a very harsh environment, where it is exposed to temperatures of several hundreds of Celsius degrees in exhaust gases flowing at very high velocities. Also in transient load stages the control on the turbocharger has considerable impact on the engine performance.
Different kinds of valve systems are disclosed in the following publications.
WO 2012/175794 A2 discloses a turbocharger and a gas flow system connecting a compressor part and a turbine part of the turbocharger unit with the engine, which gas flow system comprises at least one fluid flow control device arranged to control the flow of gas. The fluid flow control device is a digital valve system which comprises at least two parallel valve units each having two operational positions.
EP0137282 A2 discloses an EGR-system for controlling the amount of exhaust gas recirculation flow between an exhaust gas passage and the intake manifold. There is a plurality of solenoid actuated valves situated in a passage linking the exhaust gas system and the intake manifold. There is also disclosed a method comprising energizing a particular one or group of said solenoid responsive valves in a predetermined order such that the composite flow through said orifices is achieved.
U.S. Pat. No. 4,768,544A discloses a digital valve in which the valve units are operated by pneumatic piston cylinder, one of which is connected to each said valve units.
An object of the invention is to provide a digital waste gate valve arrangement and method of operating a digital waste gate valve arrangement which provides more reliable operation than prior art waste gas valve arrangements.